Printing on flat glass boards for decoration or coloring purposes involves unique techniques for feeding printing and affixing the printed image on the glass board for long term lasting on the finished product. The techniques currently known in the art for glass printing are much more complicated, and as a result—also expensive, comparing to printing methods for printing on surfaces of other materials thus often do not fit for printed glass boards in mass production and in acceptable costs. Accordingly, the market of decoratively printed glasses is not a very developed one, and thus in general a plain (i.e. not printed) glass is commonly used for doors, windows or other glass barriers. This is despite of the fact that painted glass could be a source of pleasing decoration and may involve unique effects when combined with either natural or artificial illumination designs, as could be appreciated from sites where such decoration is already in use.
The problems involved in glass printing mainly result from its surface smoothness, its material stiffness and its wet repulsion characteristics which do not allow for impressing it with conventional inks having conventional drying attributes. Accordingly, special ink compositions are used for long lasting glass printing, which commonly include nano particles of glass, wherein the fixation of the printed image is by firing the printed glass in a furnace at high temperatures of 550.degree. C. and more. The exposure of the ink to such high temperature causes the glass micro (or nano) particles to melt, thus affixing the ink pigments into the printed glass surface.
As a result, currently methods for glass printing are mainly based on screen-printing (or silk-printing, both will be referred to hereinafter as “screen-printing”) that is the only known method for handling the unique ink compositions that should be used for long lasting printing on flat glass boards.
There are several disadvantages, however, involved in screen-printing of glass boards: difficulties to meet unique customer's requirements (e.g. color, size, shape, small production series etc.) at acceptable prices; long set-up time in shifting from printing one series to the printing of another (because the screen-frame carrying the image should be discharged from the machine and replaced by another); color printing is involved with replacement of the printing frame for each color, or with the use of a series of printer units, each for a different color, with appropriate ink drying/curing stages in between. These and other disadvantages are followed by expensive human labor, equipment and production costs, materials and storage costs (prepared screen-printing frames should be stored after use for a future use of the same application, otherwise should be reproduced for every work order), which places the glass printing market at a low level compared to printing markets of other raw materials.
It is an object of the present invention to disclose an alternative printing method and a printing apparatus that will allow for replacing the traditional screen-printing machinery used in the flat glass printing industry, while solving the above-mentioned disadvantages accompanying screen-printing, and at the same time opening new markets for flat glass printing.
The method and apparatus according to the present invention are inter-alia aimed at the following purposes that are served today by screen-printing:
Automotive—vehicle's windscreens and windows have a narrow painted pattern (a frame) around their upper part, which protects the glue that attaches the window to the car frame from the sun UV radiation and decorates the windscreen;
Architecture—decorative windows for internal and external use.
Home Appliances—windows for microwave ovens, ovens, refrigerators (the invention is not limited to oversized or wide format printing).
In order to achieve the requirements of such printed patterns, which are far different from those of conventional printing (for example, for an automotive windscreens: very high temperature durability, above 550.degree. C., resistance to soaking in warm sulfuric acid and sodium hydroxide solutions etc.), the printed apparatus that should be developed should be capable of functioning with inks that become an integral part of the glass, in an industrial process, which includes heating over 550.degree. C. after the printing, and should have comfortable flexibility in printing either large or small printing series, in replacing the printed image from series to series and in changing colors and in full color printing.
The present invented method and apparatus deal and try to comply with said aims as will become more apparent from the following description.